In the Name of Research
by shimmeryshine
Summary: "God, if I can't sleep with him, can I watch you sleep with him?"  Castle/Beckett/Natalie Rhodes for the prompts watch and method


**A/N: **Written for Porn Battle XII for the prompts watch and method. It's kind of a threesome up in here ya'll!

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><p>It all starts out innocently enough, a round of shots (tequila, naturally) on Natalie Rhodes for "research" slash a thank you for indulging her company for the better part of a week, but then it turns into another and another and before long half the precinct is slammed and turning any open space of The Old Haunt into a club style dance floor. Castle's got some thumpy music playing, encouraging his usually straight laced compatriots to let loose a little bit, and it is <em>really <em>working. Even Beckett is pliant and dancing next to a tipsy looking Lanie and Esposito, twisting her body around with a kind of effortless rhythm that absolutely does _not_ escape Castle's notice. He swallows tightly as he approaches her, almost accidentally, feet propelling him in her direction without his strict permission, but there's really nowhere else at this party he'd rather be than at her side, brushing against her as she dances.

He sidles up to her, smooth with alcohol and charm and Castle confidence and leans down to whisper in her ear, voice low and private. "Drink, detective?" he asks her, maneuvering one of his hands in front of her, letting the other tip tap against her hip. They've been drinking enough for both of them to pretend the action isn't purposeful even though it _is_, so instead of moving away, she backs into it slightly and lifts the clear drink from his hand, the condensation cool against her heated skin.

"Cherry on top?" she asks him, eyebrow raised as she half turns her head so he can see her face, in case he can't hear the inflection in her voice because of the music, but he already knows the expression she wears without ever having to look.

"Because you always smell like cherries," he says like they're sharing a secret, and she already knew that but appreciates the way he knows things about her no one else cares to notice. Appreciates it _too_ much sometimes if she thinks about it for too long (which she usually doesn't). He's not moving away from her, so she turns in his grasp, facing him as she plucks the cherry off the top of the ice and drops it into her mouth with a little help from her tongue. His eyes are riveted, locked on her mouth as she holds the stem and works the berry free, chewing languidly and then slowly letting her throat contract in a swallow. His eyes follow the fruit all the way down her neck, and then further before his distracted gaze lifts back to hers. She's smirking at him.

She leans in a little bit, torturing him. "Now I'm going to _taste_ like cherries too," she breathes, practically into his mouth and then pushes past him as his strangled groan follows, searching out her wayward medical examiner of a friend. Instead of Lanie though, she almost collides with Natalie Rhodes, who is still looking freakishly like her with a brown wig and clothes that look like they could come from her own closet. Natalie's wearing a smirk like she's just unlocked some kind of huge character mystery and it makes Beckett's stomach clench a little bit because that display with Castle had been a bit _suggestive_ out of context, if she'd been watching.

She, of course, had been.

Natalie takes a long pull of her drink, letting her eyes bore into Beckett's for a string of moments that somehow serve to draw the detective in instead of warding her off. She's maybe drunk enough to find a third party's observations about her more interesting than invasive, which makes Beckett think she's probably drunker than she should be. She takes a large gulp of her own drink anyway, the remnants of cherry on her tongue making her think of Castle.

"So tell me," Natalie starts, leaning in close, conspiratorial. "You guys have _definitely_ fucked, right?" Beckett almost chokes at the actress's directness, eyes widening as she steps closer, afraid of who will hear.

"Can you not – " Beckett starts to say, eying the people around them, several cops from her own precinct, but Natalie cuts her off with an exuberant victory squeak.

"I knew it." Her voice lowers. "I knew you were the reason he wouldn't sleep with me."

Beckett rolls her eyes at the other woman's reaction to being rejected by _one_ man in her entire life, but she can't help but feel relieved again at the confirmation that Castle did not, in fact, sleep with the fictional version of herself.

"We're not…we're not together, he could have slept with you if he wanted to." Her voice is bordering on false even to her own ears.

Natalie narrows her eyes in interest and turns them around, deftly crowding Beckett backward and into a secluded corner where no one can really hear their conversation. The music thumps through her blood as she catches sight of Castle, talking to Esposito but with his eyes trained only on her. It's like he knows what they're talking about and it makes her stomach twist hotly.

"How long has it been?" she asks curiously, staring unnervingly into Beckett's eyes, studying her reaction.

"Natalie."

"Oh come on, if I can't sleep with him, I need you to give me something. It's for _research_, Kate, I just want to get Nikki Heat right."

Beckett sighs and takes another swig of her drink, feeling it burn slightly on the way down. She's too drunk to have this conversation responsibly, which is to say _not at all_, so she decides to continue on her path of intoxication in hopes of forgetting the entire thing all together.

"How long?"

"I don't know, a while? Months?" Natalie nods exaggeratedly and Beckett half expects her to pull out her Blackberry to take notes. She leans in closer again.

"How was it?"

There's a moment where Beckett thinks that this is the point where she should either bow out of this conversation or go all in, and in truth she likes being able to talk about it a little bit, since she and Castle have a very strict, unspoken rule of never, ever mentioning it aloud.

She leans in a little closer, letting the words spill from her lips in a rush. "Fast, desperate, _hot_." Her eyes close a little bit at the memory as she watches Natalie bite her lip. It's more than a little bit exhilarating to know she's got this other woman so _interested._

"God, if I can't sleep with him, can I watch _you_ sleep with him?"

Beckett can tell it slips out of Natalie's mouth without being filtered first, the other woman's blue eyes going as wide as Beckett's do, but then she's narrowing in on the brunette again, fairly trapping her against the back wall.

"_Are you serious_?" Beckett hisses, her tongue tripping around her s's as an image of Castle with his hands all over her pops into her mind unbidden, a thought that once had, takes hold with a vengeance. It's been so long and she hates that she almost wants to say yes just to _feel_ _him_ again and she's so drunk that she shouldn't be allowed to make _any_ kind of decision let alone one so absolutely _tempting_.

"I just want to…watch your face." Beckett's eyes open wider and then Natalie is waving her drink in front of their noses, a takeback. "No wait, just – we've all been drinking. What if we take a cab back to your apartment? Invite me up for coffee. If you guys can't keep your hands off each other and I just happen to be there, _researching_, then what's the harm?"

Beckett's mind glazes over, wrought with tequila and lust and she's not sure if Natalie's argument makes sense or if she's just too far gone to care. She eyes the other woman, attractive, interested, with a _legitimate_ point. A valid excuse. A _reason_.

As if on cue Castle comes tripping through the crowd to bump shoulders with Natalie and comes to rest just beside her, grinning fuzzily. He looks happy and _drunk_.

It would be so easy.

"Do you want to share a cab?" Beckett blurts out.

.

She spends the cab ride uptown sandwiched between the fictional version of herself and said fictional version's creator, sweat beading at the back of her neck as he lays a hot palm against her naked thigh like he knows exactly what's going to happen when they get upstairs. The weight of Natalie's thigh rests against her other leg, a contrast to the rough feeling of his palm, all smooth, soft skin against her own. It makes her feel warmer than the tequila, warmer than she should be, _hot_, and then the cab is lurching to a stop at her curb and someone throws a wad of cash at him and the three of them are stumbling through her building door with hands and arms and legs that belong to nobody and everybody.

.

Nobody has coffee once they make it inside. Being drunk is an excuse for this, and sobering up is appealing to exactly no one, so Beckett just lingers close enough to Castle's body to tempt him into touching her, a feigned stumble as she slips off her shoe and then his hand is at her waist and hers is fisted in his shirt and his lips are just a second away from claiming hers the way she knows he wants to.

His eyes dart to Natalie as Beckett drops a few inches, losing both of her shoes, and she looks hungry for what she's watching them do. It sends a thrill through him, being watched like this, by _her_, when she's still dressed as Nikki Heat and he groans aloud at the reality of it, feeling Beckett press her entire front to his body in response. He looks away from Natalie only then, because he can't _not_ look at Beckett's face when she's being this tactile and what he sees there is enough to make him gulp down another moan. Her pupils are blown, eyes dark like chocolate, and she looks like she wants to devour him.

"Are we…" he starts to say, flicking his eyes back to her doppelganger as he slides a palm across her back to pull her closer against him. "Is she?" Beckett's mouth ghosts against his as he tries and fails to ask the question screaming through his head, doing nothing to help his articulation.

"She's doing research," Beckett says as she finally presses her lips solidly against his once, twice, three times until she groans into it and he uses his free hand to grip the back of her head and pull her in so his tongue can climb inside of her. She gasps around it, _so good_ after so long, exactly what she wants, what neither of them can ever get from anyone else and then she's jumping up and he's helping her wrap her legs around his waist as he steadies her at the thighs and starts walking her backward toward her bedroom.

They pass Natalie by as they walk, Castle's mouth sucking warmly on the tendons of Beckett's neck, and she lets one of her hands reach out to grab for one of the other woman's, inviting her to join them without a spoken word. Natalie's fingers are warm in hers as she tugs her down the hallway, Castle ambling slowly because of her weight and the alcohol threading through his blood. Natalie bumps into his back as he stumbles against her doorframe, digging her back into the white wood a little bit as he tries to steady them.

"_Ow_," she gasps as she feels the corner of the wall line against her spine, making her arch into him. Her head lolls to the side, catching Natalie's gaze as he tries to rearrange them, stop from dropping her. Her eyes are a stormy blue that match Castle's quite nicely, and it does more for Beckett than she would have thought. She doesn't let her hand drop.

"Put me down Castle, I can walk you know." Her voice is breathless as she slides down his body, bare feet hitting the floor clumsily, and then he's tugging her through the doorway of the bedroom like they've done this a million times and they're this three linked chain of intoxicated lust and it makes her heart pound with all the blood rushing away from her head. She bumps into Castle's back as he stops at the edge of her mattress and she can see him unbuttoning the buttons of his black dress shirt, and then Natalie is bumping _her_ from behind and she bites her lip because she _thinks_ she feels lips graze her shoulder but she's not sure, and then Natalie is letting her go and crawling up to settle against her pillows and Beckett really can't keep her eyes off her.

When she speaks for the first time, it's a bit jarring in the small, dim space of the room, but then she slides over to flick on the small bedside lamp Beckett uses at night to read and the whole space is cast in a warm kind of light that makes her feel cocooned.

"Just pretend I'm not here," Natalie instructs as she watches Castle shuck his shirt and Beckett looks away for long enough to get distracted by the way he's undressing her with his eyes. His stare is all it takes to make her sit down on the edge of the bed and slide up, his body following until he's moving the hem of her dress up her thigh and over her waist and palming the skin at her hip as he raises himself over her. Beckett tilts her head back and shuts her eyes, pressing the top of her skull into the mattress as she feels him keep pulling her dress up, his fingers skimming along the naked skin of her abdomen like they're made of fire. It's too much and not enough and her knees fall open to invite him in, hips pressing up needily but finding no purchase as he keeps mouthing his way across her cleavage and up her neck and to her ear.

"Are we being Nikki and Rook right now?" he asks her, trailing the shell of her ear with the tip of his tongue and then his teeth. She grits her own as he lets a thigh slide between her legs and gives her some friction, _finally_, and then she's smoothing a hand through her own hair to try and keep it together.

He makes eye contact with Natalie over Beckett's head as he speaks to her, making sure she can hear what he's saying. Her eyes are bright and alert, wide and interested as she watches Beckett's face in the same way she'd been watching her all week in the precinct. He's a little bit surprised she's not trying to video tape this.

Before Beckett can answer him, Natalie jumps in, voice low and throaty as she presses back against the headboard. "Will you pretend to lick salt off her stomach? They changed it in the script."

Beckett's eyes pop open at the question and Castle feels her unconsciously grind against his leg, so he thinks she's into it but he decides to double check, nosing his way across her cheek again.

"Okay?" he asks as he trails a finger around her belly button suggestively.

"Yeah, do it."

Her eyes meet Natalie's as Castle heads downward and then she feels him open his mouth against her skin and _lick_, a hot, wet trail erupting across the delicate skin of her lower belly. She arches into it, head fuzzy and body almost liquefied as he tongues her and then Natalie sucks her bottom lip between her teeth and _mimics her expression_ and she almost cries out because it's a little bit like she's watching herself have sex with Castle and it's too much like a dream to be real and she's just overwhelmed and of course that's the moment when Castle decides to slide his hot palm against the front of her underwear as he finishes up his mock tequila lick, making her snap her thighs closed around him before she can stop herself.

He's trapped there and grinning at her over her knees as his head pops back up and she's swearing under her breath because she almost came and he's barely touched her. She pushes him off then, dropping her knees again, needing a moment to calm down, so she half sits up and pulls off her own dress, letting herself bounce back down to the mattress in just her underwear, the air cooling her skin a little bit. She's never been particularly shy about her body, but there's something unnervingly revealing about getting naked in front of another woman. It's almost comparative, curious, and she feels Natalie's eyes rove over her exposed skin with interest. As Castle stands up to shove his pants off, Natalie leans down to her, dragging a finger across her collarbone.

"I can see why he's written three books about you," she says loudly enough for Castle to hear. "I don't know how he keeps his hands off of you."

Beckett swallows thickly at her words, her eyes dragged back to Castle's face of their own accord. He's staring at her, _all of her_, and she can see it all over his face that he's about to unleash himself on her because during these months where they don't touch he really only barely manages it. They both only barely manage it.

She hooks a foot against his thigh to summon him back to the bed and he comes without preamble, crawling back up her body until he's kissing her mouth, all tongue and teeth, messy and desperate. Beckett hears Natalie suck in a breath as Castle's palms come up to cup her breasts, thumbs rubbing over her nipples in circles that make her arch until she's rubbing herself against the front of his underwear and then she's shoving them off, fisting him until he's gasping into her mouth and yanking her hand away by the wrist. It's good to know that he's as close as she is.

He makes quick work of her underwear too and then it's all slippery friction as she buries her face in his neck and bites down. He grunts and pulls her head back by her hair so he can kiss her, rough and deep like he means it, retaliation for her bite and then they're falling all the way back to the mattress again and he's about to slide one of her thighs over his hip when Natalie and Beckett both grunt a little bit and he realizes they've kind of ended up in Natalie's lap.

He sits back a little, enough for Beckett to scoot off of her, but Natalie doesn't seem to mind, cheeks flushed, hair a bit mussed, the hem of her dress slid precariously high on her thigh. Beckett is deliberate as she moves, placing both hands right at the curve of Natalie's knees, and if she were to lean down, she'd find herself face first in Natalie's skirt. Castle's heart pounds at the sight of it, the suggestion _alone_ enough fuel a thousand fantasies but then Beckett's letting her fingers slide down the other woman's legs and off, effectively ending the moment.

"How do you want me?" Beckett asks her, voice dripping with sex and he can see that Natalie has to stumble over the obvious double entendre before she can force out an answer. It's strangely arousing to watch Beckett hold this power over another _woman_.

"I need to see your face," she says, throat sounding dry and tight.

Beckett chews her lip for a moment, knowing that if she's facing Natalie, that would put Castle _behind _her and she's not usually one for that kind of submission, but the whole point of this encounter, the _excuse_ she'll have to feed herself in the morning is that this is for _research_, for Natalie and the movie and _Nikki_, and if Natalie needs to see her face then she's going to make it happen.

"Get behind me Castle," she throws back without breaking eye contact with Natalie, feeling Castle grip her hips tightly. She's on all fours then and his fingers are dragging moisture from between her legs and then she feels him there against her and _oh fuck_ she missed this. Her eyes slide shut as he thrusts against her, slow and deep and her skin burns with the knowledge that she's being watched. She keeps her eyes closed for a little while though, just feeling, moving against Castle's thrusts, letting her face do what it will for Natalie's benefit.

It gets harder though, after he snakes a hand back between her legs, playing with her in a way he has no right to be so good at, and her composure starts to crumble, making her head drop down and to the mattress, her face pressing into the blankets as she tries not to cry out too loudly. She feels hands against her face then, small hands with thin fingers and she knows it's not Castle, knows it's Natalie touching her, and she groans a little louder at the thought of it until her head turns so she's cheek down and her eyes open.

"Let me see your face," Natalie says softly, letting her hands tangle in Beckett's hair, eyes devouring her every expression. It's so intent, the way she's watching her, so like the way Castle does but also _different_ and then Beckett's pushing herself up onto her forearms and noticing that Natalie's dress is pushed so far up that it's obvious she's just as affected by watching them have sex as they are _having it_.

It's all instinct then, the way Beckett's fingers curl around her thighs, pulling her forward enough to reach her, and then fake brown hair is meeting real brown hair and Natalie's hot little tongue is in her mouth and they're both gasping against the kiss until she hears Castle swear obscenely behind her and tense up between her legs. She lets the other woman go with a soft pop of saliva and cranes her head backward to look at him, hips stilling as she watches him battle to control himself, eyes locked on the two of them.

"Don't you _dare_, I'm not finished yet," she commands, sounding every bit the cop and Natalie stares wide eyed as Beckett orders him not to come and he _doesn't_. Beckett turns back to her then, diving in for another kiss, as she feels Castle pick up speed both behind her and in front and Natalie's tongue tastes her desperate gasps as her back starts to bow and Natalie pries their mouths apart because she _has_ _to watch_ and Beckett doesn't even know what she looks like as she breaks apart around Castle's sure strokes with Natalie's fingers in her hair and then she's falling to the mattress as Castle frantically moves against her still, miraculously holding out as she thrums against his body. Now that Natalie's seen what she came for, this thinly veiled excuse for a threesome so weird she's sure it'll top even some of Castle's most impressive stories, she wraps one of her hands around Beckett's fingers and tugs a little bit and Beckett doesn't have to be asked twice, she slides her palm up Natalie's naked thigh and over her underwear, pressing her thumb just where she needs it in tight little circles until Natalie's arching up and into her and Castle's gripping her hips bruisingly from behind and she almost blacks out from the combined stimulation from absolutely _every_ source she could imagine.

Her cheek falls damply against Natalie's thigh as Castle collapses onto the bed next to her, all three of them panting and boneless, the mix of alcohol and sex heady and all encompassing. She feels it the second Castle notices that Natalie looks just as wrecked as the two of them, and she waits for his inevitable question as he lightly kisses a path across her shoulder blades and lays his head in the crook of her neck.

"Did you…" he trails off, eyes locked on the way Natalie's dress is shoved up and Beckett's hands are resting all too casually on her thighs.

"Just like you dreamed it?" Beckett smirks, letting her fingers rub gentle circles into the other woman's skin before she slides down to the blankets, letting her own skin cool.

He groans at her, unable to respond with words.

"Maybe next time you'll keep your eyes open, champ," she teases him as he curls around her back, both of them already drifting. Natalie scoots herself down off the pillows, knees bumping Beckett's as she gets comfortable, and she finds herself trapped in the middle of a warm Nikki Heat sandwich and it is not the least bit unpleasant. At least not _yet_, they're all still too high on endorphins to feel regret.

"There _are_ two more books to adapt," Natalie throws in, closing her eyes and pressing her nose to Beckett's hair, content.

"I'll call my agent in the morning."


End file.
